function getAjax(){
		var xhr=null;
		if(window.XMLHttpRequest){
			//非ie浏览器
			xhr=new XMLHttpRequest;
		}else{
			//ie浏览器
			xhr=new ActiveXObjext('MicroSoft.XMLHttp');
		}
		return xhr;
	}
function $(id) {
	return document.getElementById(id);
}
function $F(id) {
	return $(id).value;
}